Cryotron circuits



United States Patent O 3,364,364 CRYTRN CERCUETS Richard W. Ahrens, Somerville, NJ., assigner to Radio Corporation ot' America, a corporation of Delaware Filed Dec. 22, 1964, Ser. No. 426,289 7 Claims. (Cl. 397-2434) ABSTRACT @E THE DSCLSURE The cryotrons in the last level of a switching tree are located on opposite sides of the current paths into one of which it is desired to steer drive current. Each cryotron has a gate element on the substrate, a by-pass element joined to and located over the gate element, and a control' element which passes between the gate and by-pass elements. A control current, when present, drives the gate element on one side of a current path to the normal (resistive) state but does not aiect the superconducting state of the corresponding by-pass element. It a drive current is present at the common connection of the gate and by-pass elements at this time, it steers substantially entirely through the by-pass element to one of the current paths. This switching arrangement permits the oate elements to be relatively wide even thougr the drive lines are narrow and closely spaced.

This invention relates to cryoelectric circuits and particularly to improved cryotron circuits.

An object of the invention is to provide a new and improved cryotron selection mother object ot the invention is to provide improved cryotron switches for an arrangement of relatively narrow, relatively closely-spaced superconductor lines to one of which it is desired to apply current.

Another object or the invention is to provide a cryotron arrangement in which the current steered out of a nonselected path is employed to overdrive and thereby more quickly to quench a gate element in series with that non-selected path.

The invention is discussed in greater detail below and is shown in the following drawings, of which:

FIGURE l is a plan view of a portion of a prior art cryotron selection tree;

FlGURE 2 is a plan view of a portion of a cryotron selection tree according to the invention; and

FIGURE 3 is a perspective showing of a portion of the tree of FIGURE 2.

The showings in the various figures above are somewhat idealized for the sake of clarity. lt is to be understood that the various layers of metal are in the form of thin lilms, perhaps several thousand Angstroms thick. The various metal layers are spaced by insulation such as silicon monoxide. ln most cases, the insulation is assumed but not shown, again for the sake of drawing clarity.

The circuits to be discussed operate in a low temperature environment, such as a few degrees Kelvin. The means for providing this environment is well known and is assumed to be present.

The prior art arrangement of FIGURE l includes a plurality of thin iilm lines or paths, four of which 11-14 are shown. The lines may be formed of a superconductor material such as lead and are insulated from and over a superconductor plane. The plane may be a lead ground plane or, in the Case of a continuous lm memory, a tin memory plane. In the case of a memory, the lines may, for example, be the X drive lines of t'ne memory and, in this case, there would be Y drive lines (not shown) passing over the X drive lines, in well known fashion.

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A cryotron selection tree shown at the left in FIG- URE l is employed to apply the input current to a selected one of the lines 11-14. The selection tree includes a plurality of levels, the last level and the next-tolast level being shown in FIGURE l. Each cryotron includes a gate element, such as 1S, which is formed of a superconductor element such as tin, and a control element, such as 16, which is formed of a superconductor element such as lead. Here and elsewhere, lead and tin are specified only by way of example, as other materials may be used instead. It is only necessary that the materials be such that the gate element is capable of being driven normal (resistive) more easily than (at a lower value of magnetic iield than) the control element.

In the operation of the arrangement of FIGURE 1, currents are applied either to the 17 or O control element in each level of the tree. If it is desired to select a line such as 13, current is applied to control element 17 (a l control element) in the next-toelast level of the tree and to control element 13 (a 0 control element) in the last level of the tree. The current applied to control element 17 drives the gate element 19 to the normal (resistive) condition, and the current I thereupon steers into the path 2li. The current applied to control element 18 drives the oate element 15 normal and the current in path 29 thereupon steers through path 22 to line 13.

In one practical circuit which has been built, in the interest of obtaining close packing density, it was found desirable to make the lines l1-14 relatively narrow and also relatively closely to space these lines. In this arrangement, the line width tz is 5 mils and the spacing b between lines is also 5 mils. Accordingly, in the last level of the tree it is not possible to make the gate elements any wider than 5 mils. The amount of current I which can be carried by a gate element such as 15 is dependent upon the width a of this gate element. If the current required in a line such as 14 is too large, then that current will cause the gate element 15 in series with that line to selfquench, that is, to be driven normal even though there may he no control current present in the control element 1S associated with that gate element.

In the selection tree of the present arrangement, it is possible substantially to increase the width of the gate element without alltecting the spacing of the lines lli-1d. The improved arrangement is shown in FIGURES 2 and 3. The next-to-last level of the tree is the same as that for the prior art arrangement. It might be mentioned that this level introduces no particular problems, since adequate space is available to make the gate elements as wide as is desired. However, the cryotrons of the last level of the tree are diterent from those of the arrangement of FIGURE 1. In the improved arrangement, the pairs of cryotrons in the last level of the tree are arranged one cryotron of a pair on one side of the line to be selected and the other on the other side of said line. For example, in FIGURE 2 one of the cryotrons for paths 13 and 14 is located at 21 and the other cryotron is located at Z2.. Each such cryotron consists of a tin gate element 24 located beneath a lead by-pass element 26. The tin and lead elements 24 and 26 are joined at one edge and insulated from one another (insulation not shown in FIGURE 3) throughout the remainder of their extent. The gate element 24 is connected to one line, such as 14, and the by-pass element 26 is connected at its gate element 24a to the path 13 and at its. passes between elements 24 and 26 and is insulated therefrom by an insulator (not shown in FIGURE 3) such as silicon monoxide or the like. The cryotron 22 located on the other side of the paths 13 and 14 is connected at its gate element 24a to the path 13 and at its by-pass element 26a to the path 14.

In the operation of the arrangement of FIGURE 3, if a current is applied to control element 17a, the gate element 19a is driven normal and the input current I steers into path 20, 28. If a control current is concurrently applied to control element 3G, the magnetic field due to this current concentrates mainly between the control element 36 and the superconductor plane 31. This magnetic field drives the tin gate element 24 normal. Accordingly, the current present in path 28 steers through by-pass element 26 to the line 13. From the line f3, this current flows through the superconductive gate element 24a to the common return 32.

As one other example, if it is desired to select path 14, control currents are applied to control elements 17a and 16a. The current applied to control element 17a causes the current l to steer into path 2t), 28. The current applied to control element 16a drives the tin gate electrode 24a normal, placing a finite resistance in series with the path 13. Therefore, the current present at 28 steers through the superconductive gate element 24 to the line 14. From the line 14, the current flows through the lead by-pass element 26a to the common return 32.

There are two important advantages obtained with the arrangement of FIGURE 3. One is that it is possible to make the gate element relatively wide. if the lines ll-e are mils wide and spaced 5 mils apart, the gate elements can be made l5 mils wide and spaced 5 mils apart. Secondly, the current steered into the selected path overdrives and thereby helps to quench the gate element in series with the non-selected path. For example, when the gate element 24 is driven normal by the magnetic field of the control element 3l?, the current steers into the lead by-pass element 26. The magnetic field due to the current passing through element 26 concentrates between element 26 and the superconductor plane 32. This field therefore is also applied to the gate element 24 and aids in driving the gate element 24 to the normal condition very quickly. In other words, with the arrangement shown, it is possible somewhat to reduce the control current without adversely affecting the speed at which the gate element switches from the superconducting to the normal state.

What is claimed is:

l. In combination:

a superconductor plane;

an insulating substrate on the superconductor plane;

a first superconductor element on the substrate;

a second superconductor element lying over the opposite surface of the first superconductor element from the substrate which is joined to the first superconductor element at one edge and is insulated from the first element for the remainder of its extent, at least a portion of said first element being formed of a material which requires a substantially smaller magnetic field to ydrive it normal than the material of the second element;

means for applying a current to the common connection of the two elements which, when said portion of said rst two element is in its normal state, steers substantially entirely to the said second element; and

means for driving said portion of said first element between superconducting and normal states without changing the superconducting state of said second element.

2. In combination:

a superconductor plane;

an insulating substrate on the superconductor plane;

a first superconductor element on the substrate;

a second superconductor element lying over the opposite surface of the first superconductor element 'from the substrate which is joined to the first superconductor element at one edgeand is insulated from the first element for the remainder of its extent, at least a portion of said first element being formed of of a material which requires a substantially smaller magnetic field to drive it normal than the material of the second element;

a control element in magnetic field coupling relationship with said first element for producing a magnetic field of a magnitude sufiicient to drive said portion of said first element normal; and

means for applying a current to the region of the first and second elements where they are joined, whereby when said portion of said first element is in the normal state, said current steers into said second element, said current producing a magnetic field which also tends to drive said portion of said first element into the normal condition.

3. In combination:

a superconductor plane;

an insulating substrate on the superconductor plane;

a first superconductor element on the substrate;

a second superconductor element lying over the op# posite surface of the first superconductor element from the substrate which is joined to the first superconductor element at one edge and is insulated from the first element for the remainder of its extent, at least a portion of said first element being formed of a material which requires a substantially smaller magnetic field to drive it normal than the material of the second element;

means for applying a current to the common connection ofthe two elements; and

a superconductor control element passing between and insulated from the rst and second elements for producing a magnetic field of a magnitude suicient to drive said portion of said first element normal to steer the current applied to said common connection substantially entirely into said second element.

4l. In a cryotron switching tree,

a superconductor plane;

an insulating substrate on the superconductor plane;

a pair of lines on the substrate;

a pair of first superconductor elements on the substrate, one joined to one end of the first line and the other joined to the other end of the second line;

a pair of second superconductor elements respectively lying over the opposite surface of tthe first superconductor elements from the substrate, each second element being joined to its first element at an edge thereof opposite to the edge of the first element joined to the line, and each second element being insulated from its first element for the remainder of its extent, one second element being joined to the other end of the rst line and the second, second element being joined to the first end of the second line, each first element including at least one portion formed of a material which requires a substantially smaller magnetic field to drive it normal than the material of the second element; and

two control elements, each in magnetic coupling relationship with a different first element, each for producing a magnetic field of a magnitude suflicient to drive the portion of the first element to which it is coupled normal.

5. In combination:

first and second superconductor lines;

a first superconductor gate element connected to one end of the first line and a first superconductor bypass element lying over the gate element which is joined to the first gate element, connected to the same end of the second line;

a second superconductor gate element connected to the other end of the second line and a second superconductor by-pass element lying over the second gate element which is joined to the second gate element, connected to the other end of the first line;

means for applying a current to the first gate and by-pass elements; and

two control lines, one passing between and insulated from the rst elements and the other passing between and insulated from tbe second elements for selectively driving one of the first and second gate elements normal.

6. In combination:

a superconductor plane;

an insulating substrate on the Superconcluctor plane;

rst and second superconductor lines on the substrate;

a rst superconductor gate element lying on the substrate connected to one end of tlie irst line and a i'lrst superconductor ny-pass element lying over tbe other surface of the gate element which is joined to tbe rst gate element, connected to the same end of the second line;

a second superconductor gate element lying on the substrate connected to the other end of the second line and a second superconductor by-pass element lying over the other surface of the second gate element which is joined to the second gate element, connected to the other end of the lirst line;

means for applying a current to the rst gate and by-pass elements; and

two control lines, one passing between and insulated from the rst elements and the otl er passing between and insulated from the second elements for selectively driving one of the rst and second gate elements normal.

7. ln combination;

plurality of thin iilrn current paths, each x mils in width and spaced y mils apart; and

a plurality of cryotron gate elements respectively in series with said paths, each having a Width substantially greater than x mils and being spaced not less than y mils apart, x and y both being numbers.

References Cited UNITED STATES PATENTS 2/1966 Hageodorn 307-88-5X 2G ARTHUR GAUSS, Primary Examiner.

D. D. FORRER, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No 3 ,364 ,364 January 16 1968 Richard W. Ahrons It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 65, for "at its gate element 24a to the path 13 and at its." read to the second line 13. The Control element "1" column 3, line S9, strike out "tv/0"; line 75, strike out "of".

Signed and sealed this 18th day of March 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

